Memory card

Abstract

A memory card includes a volatile memory device, and a power supply supplying an electric voltage to the memory device while the memory card is connected to a host. A timer is started when the memory card is connected to the system. A current detector detects a current flow between a pair of terminals connected to a host. A power supply controller provided between the memory device and the power supply opens repetitively when the current detector does not detect a prescribed current flow before the timer completes a prescribed timing cycle. Thus, the memory card can be accessed only when it is connected to a host having a security function in correspondence to the memory card, while it clears the data stored therein when it is connected to a host which does not correspond to the memory card. Preferably, the current detector is activated by an active signal received from a host. The memory card may also include a timer activated when the memory card is connected to the host or when an active signal is supplied from the host. The memory card also includes at least one pair of terminals connected to corresponding terminals of the host, a current detector detecting current flow between the terminals, and a power supply controller for opening repetitively between the memory device and the power supply when the current detector does not detect a prescribed current flow before the timer completes a prescribed timing cycle.

What is claimed is: 
     
       1. A memory card comprising: a volatile memory device;   a pair of first terminals which may be connected to the host;   a power supply supplying an electric voltage to said memory device while the memory card is connected to a host through said pair of first terminals;   a timer started when a condition occurs;   at least one pair of second terminals which may be connected to the host, said second terminals being different from said pair of first terminals;   a current detector detecting a current flow between the pair of the second terminals when the pair of second terminals is connected to the host; and   a power supply controller opening a path repetitively between said memory device and said power supply when said current detector does not detect a current flowing between the pair of the second terminals before said timer completes a prescribed timing cycle.   
     
     
       2. The memory card according to claim 1, wherein the condition is connecting the memory card to the host and said timer starts when at least one terminal is connected to the host. 
     
     
       3. The memory card according to claim 2, wherein said power supply comprises a switch to stop power supply to said memory device, and said power supply controller opens repetitively the switch when said current detector does not detect a prescribed current before said timer completes the prescribed timing cycle. 
     
     
       4. The memory card according to claim 2, wherein said current detector detects a prescribed current flow between the pair of the terminals. 
     
     
       5. The memory card according to claim 2, further comprising a back up power supply including another switch to stop power supply by the back up power supply to said memory device, and said power supply controller opens said another switch when said card is connected to the host. 
     
     
       6. The memory card according to claim 2, wherein said current detector includes a resistor connecting the pair of the terminals, and said power supply controller detects a prescribed current flow through the resistor according to potentials at two ends of the resistor. 
     
     
       7. The memory card according to claim 2, further comprising two or more pairs of said terminals, wherein said current detector detects a current flow between each pair of said terminals. 
     
     
       8. The memory card according to claim 2, further comprising two or more pairs of said terminals, wherein said current detector detects a current flow between at least one pair of said terminals. 
     
     
       9. The memory card according to claim 1, wherein the condition is connecting the memory card to the host and said timer starts when at least one terminal is connected to the host, the memory card further comprising: an active signal terminal receiving an active signal from the host;   said current detector further detecting the active signal received at the active signal terminal; and   said power supply controller opening the path repetitively between said memory device and said power supply when said current detector does not detect a current flow between the pair of terminals and when said current detector does not detect the active signal at the active signal terminal.   
     
     
       10. The memory card according to claim 9, wherein said power supply includes a switch to stop power supply to said memory device, and said power supply controller opens repetitively the switch when said current detector does not detect a current flow between the pair of terminals before said timer completes a prescribed timing cycle. 
     
     
       11. The memory card according to claim 9, wherein said current detector detects a current flow of a prescribed value between the pair of the terminals. 
     
     
       12. The memory card according to claim 9, further comprising a back up power supply including another switch to stop power supply by the back up power supply to said memory device, and said power supply controller opens said another switch when the memory card is connected to the host. 
     
     
       13. The memory card according to claim 1, further comprising: an active signal terminal receiving an active signal from the host;   said current detector further detecting the active signal received at the active signal terminal; and   said power supply controller opening the path repetitively between said memory device and said power supply when said current detector does not detect a current flow between the pair of terminals and when said current detector does not detect the active signal at the active signal terminal,   wherein the condition is receiving the active signal at said active signal terminal,   said timer starting when the active signal is received at said active signal terminal.   
     
     
       14. The memory card according to claim 13, wherein said power supply includes a switch to stop power supply to said memory device, and said power supply controller opens repetitively the switch when said current detector does not detect a current flow between the pair of terminals before said timer completes the prescribed timing cycle. 
     
     
       15. The memory card according to claim 13, wherein said current detector detects a current flow of a prescribed value between the pair of the terminals. 
     
     
       16. The memory card according to claim 13, further comprising a back up power supply including another switch to stop power supply by the back up power supply to said memory device, and said power supply controller opens said another switch when the memory card is connected to the host. 
     
     
       17. The memory card according to claim 13, said at least one pair of terminals including a first and second pair of terminals, said current detector detecting a first current flow between said first pair of terminals and detecting a second current flow between said second pair of terminals,   said power supply controller opening the path repetitively between said memory device and said power supply when said current detector does not detect a first prescribed current between said first pair of terminals and a second prescribed current between said second pair of terminals before said timer completes a prescribed timing cycle.